The present invention relates to a radial tire for passenger cars having an improved durability at high speed, and high-speed steerability.
As freeway networks have increased and passenger cars have been designed to travel at high speed, tires for passenger cars should be improved in their performances in conditions of running at high speed, especially high-speed durability and high-speed steerability.
As a tire suitable for high speed driving, radial tires are widely used in which carcass cords are arranged in the radial direction and a belt layer of steel cords is effectively disposed in the tire. In such a radial tire, both ends of the belt layer are sometimes lifted and separated from the surrounding rubber due to the centrifugal force accompanying the rotation of the tire especially in high-speed driving. In particular, in the case of using a cut-end ply composed of steel cords as the belt layer, separation from the rubber is promoted together with an insufficient adhesion, and as a result the high-speed durability of the tire is lowered.
The high-speed steerability can be improved by enhancing the stiffness of the tire especially at the shoulder portion.
With the purpose of such improvements, a radial tire, for example as shown in FIG. 3, provided on each edge of a belt layer A with a narrow band layer B composed of organic fiber cords, for covering the belt layer A was proposed in Japanese Patent KOKAI No. 58-61004.
Another example, as shown in FIG. 4, providing a band layer B on the belt layer A for covering the edges there of was proposed by Japanese Patent TOKKYO KOHO No. 44-19561, and still another example in a similar constructions was offered in Japanese Unexamined Utility Model KOKAI No. 60-52503.
However, in a tire proposed in the Japanese Patent KOKAI No. 58-61004, although the movement of the belt layer A can be inhibited and the separation of the belt can be prevented to a certain degree by covering the edge of the belt layer A by the band layers B, the plurality of belt plies forming the belt layer A can be freely move relative to each other, so that the object cannot be fully achieved.
In the tires of Japanese TOKKYO KOHO No. 44-19561, shown in FIG. 4 and Japanese Unexamined Utility Model KOKAI No.62-52503, by covering the edges of the belt layer A by the band layers B, the separations of the rubber at the edges of the belt layer A can be more efficiently prevented and the high-speed durability can be enhanced in comparison with the tire shown in FIG. 3.
However, in the Japanese Patent KOKAI No. 44-19561, the folded edges of the band layer B are arranged on a plane at right angles to the tire axis which causes a drastic stiffness difference of the belt layer A on the portion of the tire and it induces uneven ground contact pressure and becomes a cause for uneven wear. Moreover, the steerability is sometimes impaired.
In the example of Japanese Unexamined Utility Model kOKAI No. 62-52503, it is proposed to arrange the cords of the band layers B parallel to the circumferential direction of the tire. It becomes apparent that in such a tire having the cords of the band layers B arranged parallel to the circumferential direction of the tire, the stiffness in the shoulder portion tends to rise excessively to cause a lack of balance and thus the steerability of the vehicle at high speed is lowered.